This invention relates to electric power cables of the kind having at least one metallic conductor, usually a conductor screen of semiconductive material, and insulation all enclosed in an earth screen comprising wires or narrow tapes and an external sheath comprising polymeric material which will usually (but not necessarily) form the exposed surface of the cable.
In most environments, it is desirable, if not essential, that the sheath is more effectively watertight than can be achieved with polymeric material alone, and attempts have thus been made to follow the practice used in communications cables of including a metal/plastics laminate foil beneath the main body of the sheath, so as to become bonded to it, normally when the main polymeric body is extruded. It is difficult, with such structures, to design a sheath in which the laminate foil remains intact when the cable is subjected to the impact tests specified by Standards Authorities and customers, as the laminate tends to be driven into the gaps between the wires or tapes of the screen and to split along resulting crease lines.